Chrome tanning-bath.



UNITED STATES Patented May 10, 1904..

PATENT OFFICE.

CLAUDE A. O. ROSELL, OF NEW'YORK, N. Y.

; CHROME TANNING-BATH.

SPECIFICATION forming part of Letters Patent No. 759,831, dated May 10, 1904.

Original application filed August 11, 1896, Serial No. 602,431. Divided and this application filed August 26, 1902. Serial No. 121,088. (No specimens.) I

To all whom it may concern.-

Be it known that l, CLAUDE A. O. ROSELL, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful improvements in Chrome TanninglBaths; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will. enable others skilled in the art to which it appertains to make and use the same.

This invention consists, essentially, in cansing a skin to take up chromic oxid directly from solutions of certain salts of chromic oxid, as will now be fully explained in the subjoined description and the appended claims.

The solutions of chromic-oxid salts of which I make use are thiosulfate, commonly called hyposulfitc, sulfite, and other reducing sulfur salt of chromium. These salts can be i made in a number of ways. such as adding the desired acid to ehromichydrate or by decomposing chromium sulfate with a suitable salt to effect metathesis or so-called double decomposition. If asalt of calcium and barium be used, the sulfate formed is insoluble and is precipitated. If, again. a sodium salt be used, the sodium sulfate will remain in solution with the chromium salt formed. As the presence of sodium sulfate in the chromium solution is entirely unobjectionable, it will be found preferable in practice to prepare the desired tanning solution by addinga suitable sodium salt to common chrome alum, which is chromium potassium sulfate. A solution ofchromium sulfitemay be formed according to'the following equation:

The reaction seems to hecomplete, because the solution prepared as above is in no wise inferior to a solution of pure chromium sul- On the-other hand, if a solution be made of chromium sulfite and chromium sulfate it is observed that with the increase of the percentage of chronium sulfite the tanning action of the bath is'improved, while the contrary effect is produced by'increasing the percentprepared as abOW3 will be found to give good results, such solutions difi'er quite considerably between themselves. It may be stated that a thiosul-fate solution has been found superior to a su'lfite solution and a mixture of the thiosulfate and sulfite solution has been found superior to any other thus far tried.

in making use of any of the above solutions the skin may be introduced directly from the bate after washing or it may be prepared in any desired way. Thus if a skin is only partly tanned by vegetable or mineral tanning material theta'nning may be completed inl any of the above baths of chromic-oxid sa ts.

If a skin is first subjected to the action of chromic acid and is afterward immersed in the above bath of chromic-oxid salt or salts, two reactions will be found to take place. In the first place chromium trioxid is reduced to chromic oxid. and the reducing acid of the chromic-oxid salt is oxidized. The following equation explains the reaction:

In the second placethe skin will take chromic oxid from the solution of chrom1coxid salt.

Although the solutions of chromic-oxid salts described are initially normal, they become acid in the proportion as ehromieoxid is abstracted by the skin from the chromic oxid salt used, leaving the solvent acid behind in a free state. As the acids I make use of are quite. innocuous, the skins as they are tanned are not in the least injuriously affected by said liberated acids.

As before stated, the tanning-bath of chro mic-oxid salt described may be used as a single bath or may also be used in connection with a chromic-acid bath.

As a single bath, the above tanning solution has the advantage of producing a more evenly and thoroughly tanned and a less corroded skin than any other tanning liquid known. If this chro'mic-oxid liquid is used in conneea reducing agent converting the chromium tion with a chromic-acid bath, this process has several important advantages.

Heretofore skins have been tanned by immersion first in a bath of chromium trioxid (generally called chomic acid) and subsequently ina reducing-bath, whereby the chrosuch processes a portion of the chromium trioxid taken up by the skin in the first bath is washed out and lost in the second bath, and to provide for this loss an excess of chromium trioxid must be employed. For these reasons it is necessary to subject the skin in thefirst bath to a very strong solution of chromic acid,

and since the latter is very corrosive this fea-- ture of the process is objectionable.

In my process when carried on by means of two baths it is necessary to impart to the skin in the chromium-trioxid bath only oneehalf to one-quarter of the c omium it is finally going to retain as combined chromic oxid,'the balance of the chromium being supplied by the second or the reducing bath, consisting of a solution of the described salts of chromic 'oxid. It therefore follows that a skin tanned by my two-bath process is subjected to less than half the corrosive action to which askin is subjected that is tanned by any Lother'twobath process 41. 8., being first subjected to the action of chromium trioxid and afterward to trioxid into chromio oxid.

1 esses on reducing the absorbed'chromium tri- If in any of the old two-bath chrome procoxid of a skin it is found to be insufiiciently tanned, the skin is hopelessly ruined. By the use of my solution of a chromic-oxid salt such imperfectly tanned skins may be saved, as they Wlll take up sufficient chromic oxid from such a solution to effect a completion of the tanning, provided they have not -been-dried,

in which case the hide will be tanned by sub-.

stantially the following process: The skin having taken up in a chromic-acid bath less than the requisite amount of chromium to complete the tanning will be immersed in any of the old 7 known reducing-baths, such a bath giving off sulfurous' a cid, hydrogen sulfid, .&c. After I this, before, drying, it will be put into a bath containlng any of the described reducing salts of chromium in quantity sufficient to complete the tanning.

Havinggiven a general outline of the'm'an-- ner 'ot fbrming the tanning solution, of its action and advantages, 1 will now give some practical data for using the process on a large scale.

In using the chromic-oxid solution as as inglebath I proceed as follow: One hundred pounds of bated and washed skins in a wet state are immersed in fifty gallons of solution containing from two per cent.- to five per.v

cent. of chrome-alum, equal parts of sodium thiosu'lfate and sulfite in quantity suflicient to decompose all the chrome-alumc'. 6., from 0.6 per cent. to 1. 5 per cent. of eachthe thiosulfate, and sulfite./ The skins are kept in motion in this solution and will be completely tanned in from two to four days, depending upon the character and size of the skins. Theskins are then washed and finished in ordr nary and approved ways. In place of adding all the chemicals at once they may be added from time to time, and in'place of using asolution of the strength stated two or three baths may be used of one-half or one-third the strength, respectively.

In using the solution of chromic-oxid salt in connection with a chromium -trioxid solutionI proceed as follows:, One hundred pounds of hated and washed skins in a wet state are immersed in fifty gallons of a solution of three-fourths per cent. potassium bichrornate and enough sulfuric acid to produce a mixture of chromic acid and potassium sulfate. After beingagitated in this solution from three to twenty-four hours the skins are re-' moved and preferably struck out, after which they are immersed in fifty gallons of liquor containing" from two and one-half to four per cent. of chrome-alum and "equal parts of sodium thiosulfate and sulfite in quantitysufiicient to just decompose all of the chrome-alum j or to leave an excess of ten per cent. to fifteen per cent. of the sodium thiosulfate and sul- Thus if the amount of chrome-alum be two and one-half per cent. to a solution of fifty gallons there would be added'chromealum, ten pounds; sodium thiosulfate, three to 7 three and 'one-half pounds, and sodium sulfite, three to three and one-half pounds, The skins are agitated in this solution from one to three days, depending upon the character and size of the skins, which'are then washed and finished as before stated. 7 It should be observed that the proportions throughout thedescription are simply by way tation. I

chromium trloxid a is men- Whenever of example and notintended to na'ke any limitioned, it should be understood that by this term is included not only chromium trioxid in-a free state, but also combinations thereof,

.such as the bichroma'tes.

When any of the solutions above described is used as a single bath, it is evident that the reducing power thereof is-not called into req-" uisition. .In such a case the bath, nevertheless', has the important advantage that the skins tanned are not in any way in uriously affected by the acid set free by the operation 3. A tanning-bath compounded essentially of tanning, the only function of the acid beof a solution of chrome-alum, a thiosulfatv fore being set free having been to keep the and a sulfite.

chromium in solution. In testimony whereof I have aflixecl my sig- 9 What 1 claim [is-inature in presence of two witnesses.

1. A tanningat 1 containing an inorganic w reducing sulfur salt of chromium. (JLAUDP ROSLLL 2. A tanning-bath consisting essentially of \Vitnesses:

a solution of chromium thiosulfatc and chro- REEVE LEWIS,

1 mium sulfite WM. B. ORKANE. 

